(a) Field of the Invention
The present invention relates to a display device and a circuit board therefor, and in particular, to a liquid crystal display and a circuit board including a plurality of interconnections for signal transmission.
(b) Description of Related Art
Flat panel displays such as liquid crystal displays (LCDs) have been developed and substituted for cathode ray tubes (CRTs) since they are suitable for recent personal computers and televisions, which become lighter and thinner.
An LCD representing the flat panel displays includes a liquid crystal panel assembly including two panels provided with two kinds of field generating electrodes such as pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed therebetween. The variation of the voltage difference between the field generating electrodes, i.e., the variation in the strength of an electric field generated by the electrodes changes the transmittance of the light passing through the LCD, and thus desired images are obtained by controlling the voltage difference between the electrodes. A typical LCD includes thin film transistors (TFTs) as switching elements for controlling the voltages to be applied to the pixel electrodes, and a plurality of display signal lines for transmitting signals to be applied to the TFTs.
In addition, the LCD further includes a printed circuit board (PCB) provided with a plurality of circuit elements. In particular, a signal controller for processing image signals from an external source and generating control signals for controlling the image signals and a voltage generator for generating a plurality of source voltages used for generating various signals are mounted on the PCB in forms of integrated circuit (IC) chips.
The liquid crystal panel assembly and the PCB are connected via a plurality of tape carrier packages (TCPs) arranged in series. The TCPs are provided with a plurality of data driver ICs for converting the image signals into the analog voltages to be applied to the pixel electrodes under the control of the signal generator.
For electrical connection between the circuit elements on the PCB and the data driver ICs, a plurality of pad areas including a plurality of parallel conducting lines and a plurality of parallel interconnections connecting the conducting lines on the adjacent pad areas are provided on the PCB, and a plurality of conductive lines to be connected to the conducting lines of the PCB are provided on the TCPs.
In a typical LCD, the image signals from the signal controller are sequentially transmitted to the data driver ICs through the interconnections between the signal generator and one of the pad areas and then through the interconnections between the pad areas. For example, when first to tenth TCPs mounting the data driver ICs and corresponding pad areas are provided, the image signals from the signal controller required for the second data driver ICs pass through the interconnections between the first pad area and the second pad area and reach the second TCP, those required for the third data driver ICs pass through the interconnections between the second pad area and the third pad area as well as the interconnections between the first pad area and the second pad area, and so on.
In this case, there is a problem that the interconnections on the PCB are very long and curved many times and thus cause electromagnetic interference (EMI) and complexity of the wires of the PCB, which is especially severe for high resolution and large-sized LCDs. For example, the interconnections between the pad areas have four turning points since both the pad areas and the conducting lines on the pad areas are arranged in the same direction and thus the parallel interconnections are connected between an upper edge of one pad area and a lower edge of the adjacent pad area for preventing intersections of the interconnections. That is, the interconnections start upwards from the conducting lines of one pad area, turn right toward the other pad area, turn down between the pad areas, turn right toward the other pad area, and finally go upwards to the corresponding conducting lines of the other pad area.